Phospholipids and water

Question 1

What are membranes composed of?

Answer 1

Phospholipids that has a hydrophilic head and a hydrophobic tail

Question 2

What is the most common phospholipid

Answer 2

Phosphoglycerides

Question 3

What is a phospholipid head and a phospholipid tail made out of?

Answer 3

Head = glycerol 
Tail = hydrocarbon chain

Question 4

What 3 main structures can phospholipids form?

Answer 4

Micelle
Liposome
Phospholipid bilayer

Question 5

Why do phospholipids form micelles in aqueous solution

Answer 5

Amphipathic

Question 6

Water and phospholipid interaction

Answer 6

Hydrophobic regions do not interact with water which increases order of water molecules therefore the formation of micelles in thermodynamically favoured

Question 7

Second law of thermodynamics

Answer 7

Entropy (disorder) can only increase

Question 8

Aggregation in phospholipids

Answer 8

In an unaggregated state the water population is highly ordered, low entorpy, energetically unfavoured.

In an aggregated state water is less ordered as hydrophobic area is reduced, higher entropy, favoured

Question 9

Are membrane lipids mobile?

Answer 9

Yes

Question 10

How can lateral diffusion of phospholipids be demonstrated and measured by?

Answer 10

Fluorescence recovery after photobleaching (FRAP)

Question 11

FRAP

Answer 11

Fluorescence recovery after photobleaching
Fluorescently tag phospholipids, take confocal microscope and select area in the cell and hit with a high intensity laser. These cannot fluoresce anymore as they are bleached. Over time the mobile phospholipids move around out of the selected area so ercovery is seen.

Question 12

Requirements for FRAP

Answer 12

Moving objects must be labelled with fluorophore

Equipment must be able to bleach a defined area

Question 13

Conclusions from FRAP

Answer 13

Diffusion of molecules
Active movement of cell components
Recycling of cell components

Question 14

Summarise FRAP in 3 steps

Answer 14

Label
Bleach with laser
Fluorescence recovery

Question 15

Is all protein movement random?

Answer 15

No

Cytoskeleton confinement
Directed motion
Transient confinement
Random diffusion

Question 16

Glycerol

Answer 16

3 Carbon alcohol with 3 OH groups

Backbone of phospholipid

Question 17

Glycerophospholipid

Answer 17

Made up of:
Glycerol 
Fatty acids
Phosphate 
Alcohol

Question 18

Monoglyceride

Answer 18

Formed from a condensation reaction between a fatty acid and the carbon 1 on the glycerol

Question 19

Diglyceride

Answer 19

Formed from a condensation reaction between carbon 1 and carbon 2 and fatty acids

Question 20

Phosphatidate

Answer 20

Addition of a phosphate to the carbon 3 to a diglyceride

Question 21

Phosphatidylethanolamine

Answer 21

Alcohols added to the phosphate group of a phosphatidate

Question 22

4 Steps to phospholipid synthesis in the ER

Answer 22

Fatty acid tails are linked to coenzyme A
Fatty acid tails are transferred to carbon 1 and carbon 2 of glycerol-3-phosphate by acyl transferase to form phosphatidic acid
Carbon 3 is dephosphorylated to form a diacylglycerol by the enzyme phosphatase
An alcohol head group is transferred from CDP-choline by choline phosphotransferase to the carbon 3 to form phosphatidylcholine

Question 23

Where does phospholipid metabolism occur?

Answer 23

Phospholipid synthesis enzymes are embedded in the smooth ER, the substrates are in the cytoplasm. Phospholipid synthesis only occurs on the outer leaflet of the membrane. Flippase enzyme moves the membrane lipids from one leaflet to the other phospholipid bilayer.

Question 24

Different alcohol head groups can be added to incorporate different chemical properties which affects which 3 things?

Answer 24

Interactions with other molecules
Packaging in lipid bilayer (fluidity)
Other physical properties (curvature)

Question 25

How does phospholipid composition determine membrane curvature?

Answer 25

Cylindrical phospholipids are associated with a flat membrane
Conical phospholipids are associated with curved membranes

Question 26

What do double bonds in fatty acids cause?

Answer 26

Kinked unsaturated phospholipids which prevents packing

Question 27

Compare oleic and stearic acids

Answer 27

Both have 18 carbon fatty acids
Stearic is saturated with a higher meltingpoint
Oleic acid has one double bond

Question 28

What do unsaturated phospholipids have lower melting points?

Answer 28

Kinks reduce the order and reduce van der waal interactions

Question 29

Do short chains or long chains have higher melting points?

Answer 29

Longer chains create higher melting points as there are more points of contact and van der waal forces needed more heat to be disrupted.

Question 30

Differential scanning colorimetry

Answer 30

Detetcs heat consumption associated with phase transitioning - changing between states

Question 31

Compare long carbon chain and short carbon chain phospholipids

Answer 31

Long: more hydrophobic, more van der waal forces, pack tightly, more gel like

Short: less hydrophobic, less van der waal forces, pack loosely, more fluid

Question 32

Sphingolipids

Answer 32

based on sphingosine
long chain amino acids
Second hydrocarbon tail added to an amide bond, phosphate and alcohol head added to C1
Usually saturated- pack closer and have different physical properties

Question 33

Cholesterol

Answer 33

Interacts with the fatty acid tail of the phospholipid.
Introduces order into the tail region for tight packaging but maintains fluidity

Amphipathic, small head group (OH), does not form bilayers on its own, 4 ring structure

Question 34

Cholesterol equivalents in plants and fungi

Answer 34

Plant: stigmasterol
Fungi: Ergosterol

Question 35

What does cholesterol preferentially bind?

Answer 35

Sphingolipids, more stable interaction between stiff flat steroid of cholesterol and long saturated fatty acid tail.

Question 36

How do you prove that cholesterol preferentially binds sphingolipids?

Answer 36

Make an artificial liposome containing fluorescently labelled phospholipids and cholesterol. It is seen that there is an equal distribution of phospholipids and cholesterol.
If you make an artificial liposome containing fluorescently labelled phospholipids, cholesterol and sphingolipids, The cholesterol partitions into islands as the cholesterol preferentially binds to sphingolipids.

Question 37

What are microdomains?

Answer 37

Lipid rafts that recruit specific proteins.
Rich in sphingolipids and cholesterol
Detergent resistant
Concentrated thicker domains

Question 38

Raft select proteins

Answer 38

Rafts are thicker than the rest of the membrane. Proteins with long transmembrane domains partition to rafts - as it is more stable for them to be here
Short domains that partition to phospholipid domains
Recruit proteins with lipid anchors or long transmembrane domains